How did the earth end up completely dry again? What happened to the water cycle? And surely a dry world would be much more suited to the types of technology required to make decontamination kits and water purifiers? Are they going to have crazy floating factories to make all of these kits?

I'm thinking more about what we're likely to witness in our lifetime. The consequences of some sort of planet wide super-crazy-drought where water's so scarce that there isn't adequate drinking water probably would be worse than a Waterworld style scenario.